1. Field of the Invention
This invention relates to a surgical instrument for piercing or puncturing a wall of body tissue to provide communication with the inside of an anatomical cavity, and more particularly this invention relates to a powered trocar with an optional safety feature for preventing the unintended puncturing of body tissue.
2. Background of the Art
Many medical procedures gain access to the inside of an anatomical cavity by using an implement such as a trocar, cannula or needle having a sharpened point to pierce or puncture the bodily tissues, muscles and membranes forming the cavity wall. A surgical needle, for example, connected to a catheter may be used to pierce a cavity (blood vessel, subarachnoid space, heart ventricle). After piercing the cavity, the needle is left in situ and used to inject or withdraw gaseous or liquid phase fluids from the cavity. similarly, in several endoscopic procedures, a small incision may be made in the skin of a patient along the abdomen for example, and the sharp point of a larger penetrating implement such as a trocar of suitable length and diameter is inserted into the incision, and pushed until the point punctures the cavity wall. Then, a sleeve follows the implement into the puncture wound to preserve the shape of the passageway created by the implement. After the sleeve is in place, the implement may be withdrawn and an endoscope and operating instruments may be inserted via the sleeve to view and operate upon organs within the cavity. Endoscopic instruments are those instruments having a relatively narrow and elongated portion for use in endoscopic surgical procedures wherein such instruments create or are inserted through a small diameter puncture in order to carry out surgical procedures within a human or animal body.
Penetrating the wall of an anatomical cavity with a surgical puncturing instrument can be quickly done and, usually creates a small neat passageway providing communication to the interior of the cavity. While the sharp point of a penetrating implement is being pushed through a cavity wall, it encounters great resistance from the tissue, muscle and membranes forming the cavity wall. Once the sharp point and blade of the implement pass through the cavity wall and into the cavity, the resistance drops significantly. The sharp point of the implement, however, can easily injure organ structure within the cavity upon the slightest contact. Unless a surgeon stops pushing the implement just as soon as penetration is complete, there is a risk that the implement will continue penetrating deeply into the cavity and injure neighboring organ structure. If an unintended bodily member is injured by the point of the implement, there is a risk that the injury may not become apparent until after completion of the surgery. At a minimum, such an injury will delay a patient's recovery. Severe injuries of this type may endanger the patient's health, and corrective surgery may be required.
Various instruments have been developed to deal with this problem. For example, U.S. Pat. No. 4,601,710 discloses a surgical instrument having a spring biased movable shield which retracts into a cannula to expose the sharp trocar tip when pressed against body tissue, but which moves forward to protect body tissue from contact with the trocar tip when the instrument has passed through the wall of body tissue.
While the instrument described in U.S. Pat. No. 4,601,710 provides an added degree of safety as opposed to an instrument without a shield, the aforementioned problem remains: the sudden drop in the resistance to the trocar blade when penetration has been made into the body cavity increases the chance of uncontrolled continued penetration and possible damage to the underlying body tissue. Moreover, tissue trauma may result from the shield. To alleviate this problem a powered trocar has been developed.